Arc welding is a process of joining metals through deposition of molten metal to a workpiece using an arc between a consumable welding electrode and the workpiece. The welding electrode is directed by a wire feeder toward the welding operation in the form of a continuous wire fed through a welding torch cable from a wire supply, and an arc is generated at the torch between the end of the electrode and the workpiece for melting and depositing electrode material to a weld in a controlled fashion. Many arc welding processes, such as metal inert gas (MIG) techniques, employ an external inert shielding gas such as argon around the welding arc to inhibit oxidation or nitridation of the molten metal. Non-inert external shielding gases such as CO2 may also be used, whereby such processes are sometimes generally referred to as gas metal arc welding (GMAW). Other arc shielding processes similarly provide a protective shield of vapor to cover the arc and slag to protect the molten weld pool as it cools. The molten electrode material may be transferred to the workpiece by several mechanisms or processes, such as short-circuit welding, spray arc welding, and pulse welding.
Cored welding electrodes are welding consumables having a tubular core or interior region surrounded by an outer sheath, where the core may include fluxing elements (e.g., flux cored electrodes), deoxidizing and denitriding agents, alloying materials, and elements that increase toughness and strength, improve corrosion resistance, and stabilize a welding arc. Flux cored arc welding (FCAW) processes employ flux-cored electrodes which include flux within the electrode core to produce an extensive slag cover during welding, where the slag protects and shapes the resulting weld bead as it cools. Such cored electrodes are typically constructed beginning with a flat metal strip that is initially formed first into a “U” shape, for example, as shown in Bernard U.S. Pat. No. 2,785,285, Sjoman U.S. Pat. No. 2,944,142, and Woods U.S. Pat. No. 3,534,390. Flux, alloying elements, and/or other core fill materials are then deposited into the “U” and the strip is closed into a tubular configuration by a series of forming rolls. As in GMAW processes, the flux-cored process uses a gas shield to protect the weld zone from detrimental atmospheric contamination (e.g., particularly from oxygen and/or nitrogen), where the shielding gas can be applied externally, or it may be generated from the decomposition of gas forming ingredients contained in the electrode core itself (sometimes referred to as a self-shielding flux cored electrode). In such self-shielded FCAW, the heat of the arc causes decomposition and some vaporization of the electrode's flux core, which partially protects the molten metal.
Various types of flux-cored welding electrodes are designed for self-shielding and externally shielded FCAW applications. In all types of cored welding electrodes, it is desirable to minimize the amount of moisture in the core fill material, to prevent adverse effects in the finished weld joint. One such moisture-related problem is known as “gas tracking” or “worm tracking”, in which marks or tracks appear as a series of depressions in the shape of a “worm” on the weld surface. This situation is caused by gases being trapped under the slag as the weld solidifies, where the slag cools and solidifies before the gas can escape. Gas tracking is at least partially worsened by moisture in the flux core of the flux cored electrodes. Encroachment of moisture into a cored electrode interior may result from various causes, including poor joint seal in the electrode manufacturing process, storage of the electrode in a damp environment, and/or unprotected wire being exposed to humidity when loaded on the wire feeder spool of a welding system. Efforts to reduce gas tracking and to otherwise combat excessive cored electrode moisture include preheating the flux cored electrode, either by external preheating apparatus prior to use and/or by employing longer wire stick out distances or contact to work distances (CTWD) in the welding process itself to thereby preheat the electrode using the weld current. However, external heating sources are costly in terms of energy and welding system space limitations, and longer CTWD may limit the performance of the welding process in other respects. Another problem in FCAW processes is diffusible hydrogen, which is worsened by moisture in the flux cored electrode. Increased diffusible hydrogen in the weld metal leads to increased cracking when the weld metal solidifies, wherein solid electrode welding has thus far been preferred over FCAW for military and other welding applications in which high strength weld joints are needed. Consequently, there is a continuing need for improved cored welding electrodes and manufacturing methods by which electrode core moisture can be mitigated or eliminated.